Since OLC is in the form of spherical particles having a diameter of from several nanometers to several tens of nanometers, exhibit a significantly low coefficient of friction both in air and in a vacuum and have good bearing resistance, they are expected to find applications as solid-state lubricants in particular. An example of methods for manufacturing such OLC is disclosed in, for example, Patent Literature 1. According to this technology, diamond nanopowder (hereinafter referred to as DNP) having a particle diameter of from 4 nm to 6 nm is produced by shock synthesis (detonation synthesis). This DNP is then hot-processed in an inert gas atmosphere at a temperature of from 1,600° C. to 1,800° C., which results in OLC.